Integrated circuits are produced in large numbers on single wafers of semiconducting material such as silicon. A wafer is cut into many pieces, each of which contains an integrated circuit (IC) and each of which is called a die. An integrated circuit die is typically mounted to a carrier substrate such as a ball grid array (BGA) through wire bonding or flip-chip mounting. In wire bonding, small pads on the IC die are attached to the BGA, for example, with small wires soldered or welded at one end to an IC die pad and at the other end to a BGA pad or connection point. In flip-chip mounting, an IC die is configured as a flip-chip with pre-processed bond pads on which solder bumps are typically formed, enabling the face-down attachment of the flip-chip to the BGA pads or connection points through, for example, ultrasonic or reflow solder processes.
Ball grid arrays (BGAs) are often used on high pin-count application specific integrated circuits (ASICs) and they comprise beads of solder between two generally circular pads for attaching the integrated circuit to a printed circuit board (PCB). Various stresses such as transportation vibration and cyclical mechanical and thermal loading on the BGA substrate, the PCB, and/or the IC die itself can cause solder joints to crack, thereby causing various pins of the integrated circuit to become detached or otherwise loosened from the PCB. These pin connection failures typically occur in the solder ball joints between the BGA and the PCB, but they can also occur in the solder joints between the IC die and the BGA for both wire-bonded and flip-chip mounted configurations.
In order to reduce the pin connection failures associated with cracked solder ball joints, corner balls of a BGA are sometimes replaced with dummy balls that are not used by active (i.e. functional) pins of the integrated circuit. Thus, if the corner dummy balls become cracked, loosened, or otherwise damaged, performance of the integrated circuit is not compromised. However, damage is not necessarily limited to the corner solder ball joints. For example, although a cracked solder ball joint may initially occur at the corner of the BGA, the cracking condition tends to propagate inward toward the center of the BGA, thereby compromising non-dummy solder ball locations associated with active pins of the integrated circuit. Furthermore, damage may also occur in other solder joints associated with active pins of the integrated circuit, such as in wire-bond and flip-chip solder joints.